In the first study of its kind to look at both maternal diabetes and maternal obesity, the researchers found that children born to women who are both obese and diabetic are four times more likely to have ASD than those born to women of healthy weight without diabetes. Obesity without diabetes and diabetes without obesity were each associated with a slightly higher risk of having a child with ASD.

ASD is a disorder of brain development often characterized by problems with social interaction, communication and repetitive behaviors. The prevalence of ASD has risen tenfold in 40 years, according to the U.S. Centers for Disease Control and Prevention (CDC), which identifies 1 in 68 American children as on the autism spectrum.

Researchers looked at 2,734 mothers who had their children at Boston Medical Center between 1998 and 2014 and had at least one follow-up visit to BMC. Of those, 102 children received a diagnosis of ASD. The research, a prospective birth cohort study, relied on medical data rather than memory, says one of the study's authors Anne Riley, a public health professor at Johns Hopkins. The women weren't asked if they were overweight at the time of pregnancy, for example (because, frankly, who would answer that honestly). Instead, researchers examined the medical records of the women who agreed to participate in the study and the records of their children as they grew up.

The researchers weren't surprised by the findings. “The fact that the multiplier effect of obesity plus diabetes was so strong, and that both of those things are really at epidemic proportions in this country now, it wasn't as much a surprise as just a major public health concern because a lot of women are obese going into pregnancy,” Riley says.

So why was there a connection between these conditions and autistic babies? The study notes that obesity increases circulating proinflammatory cytokines (these are substances in cells in the immune system) in pregnant women. Rat models showed that inflammation from obesity could lead to rat offspring having brain inflammation. Maternal diabetes also induces a proinflammatory environment. And inflammation in the uterus as well as of the fetal brain has been implicated in the development of ASD. "Co-occurring obesity and diabetes may be 'multiple hits' to the developing fetal brain, conferring an even higher risk of ASD in the offspring than a single condition," say the study authors.

Riley cautions that the increased risk of autism is only slight. “The majority of obese women are not going to have a child with ASD,” she says. If the normal autism rate is 1 in 68 children, the rate for women with diabetes and obesity before pregnancy would be 3.9 or 4 in 68 children, she says.

However, she adds, “If you're overweight, you're more at risk for Type 2 diabetes. The combination, both being overweight and having diabetes slightly increases your risk of autism based on this one study. The biggest thing you can do is avoid becoming very overweight and that will very much reduce your risk of diabetes.”

Now That’s Interesting

The United States ranks 61st in the world for maternal health, so Riley hopes that this study and others will get people talking more about pre-conception health, those things women can do before becoming pregnant to help ensure healthy outcomes for their babies.